JOHANNESBURG (miningweekly.com) – Mpumalanga-based Two Rivers, a joint venture between diversified miner African Rainbow Minerals (ARM) and platinum producer Impala Platinum (Implats), reached an important milestone last year, producing more than 400 000 oz of platinum-group metals (PGMs) for the first time since the mine started production in 2008.

Two Rivers platinum mine GM JJ Joubert tells Mining Weekly that the mine has continuously improved its year-on-year production performance over the past five years, from about 300 000 oz in 2011 to 400 722 oz in 2016, which he attributes to the continued increase in rock-face availability, the nature of the orebody, the mine design and mining 24/7.

The ore reserve is very stable, with a low dip, allowing for mechanised equipment to be deployed, thereby “setting it apart from most platinum mines”, he states.

“If an orebody does not allow for proper mining techniques, it becomes difficult to be productive. Two Rivers has a forgiving orebody that is helping us apply aggressive mining methods.”

Joubert adds that the success of the Two Rivers mine design is its simplicity, practicality and layout effectiveness. Joubert and ARM Platinum CE Francois Uys assert that the characteristics of the orebody lends themselves to the bord-and-pillar mining method used at the mine.

Joubert explains that the board sizes at Two Rivers vary from 6 m to 12 m, depending on the depth and support requirements. Ore is transported through strike belts feeding a decline shaft belt.

“It is as straightforward as you can get and there is really no complexity in the mining method,” Joubert asserts.

He adds that the bord-and-pillar mining method was selected because of the quality and characteristics of the orebody, which sits at between 8º and 9º, and is 1.8 m to 3.5 m high, making it ideal for using midtier mining equipment.

Two Rivers lies on the upper group two, commonly known as the UG2, and the Merensky reef horizons of the Bushveld Igneous Complex, which runs through the North West, Mpumalanga, Limpopo and Gauteng.

Joubert notes that, because the mine operates continuously, with blasting taking place twice daily, it can adopt an operating method that uses the mining equipment to the best of its capabilities and efficiencies.

“The equipment, layout and people are in place, and the small incremental optimisation projects are continuing to yield these results. We forecast that we will break [the Two Rivers production] record again this year.”

He adds that the 2017 production target for the mine is 380 000 oz, “but our forecast is well in excess of that . . . so we should exceed the target quite comfortably”.

It is also one of the lowest-cost producers in the platinum industry, with ARM Platinum operations executive Vusi Khumalo pointing out that the mine can produce 1 t of UG2 ore at a cost of between R600 and R650.

“The unit cost of production is mining’s biggest enemy and Two Rivers is meeting the challenge of getting that down,” adds Uys.

OPTIMISATION PROJECTS
Joubert points out that several fleet optimisation projects have been conducted at Two Rivers, which further contributed to the continued production increases at the mine.

He explains that one such programme involved replacing 5 t load-haul-dump (LHD) trucks with larger 8 t LHD trucks, which significantly increased the amount of ore moved at the mine, while reducing congestion underground, as two 8 t LHD trucks are committed to a mining level rather than three 5 t LHD trucks.

Two Rivers has 19 operational fleets, with each fleet consisting of a single-boom drill rig, two 8 t LHDs, mechanical bolters and a utility vehicle that is used to charge the rock face with emulsion and move equipment up and down the mine shafts. One fleet produces about 18 000 t/m.

Joubert also attributes the effectiveness of the mine equipment to the “exceptionally good” work of the engineering teams at Two Rivers. He points out that a significant amount of work has been done on the operating structure of the mine: “We put a lot of effort into our structures underground to ensure that the right equipment is resourced to the right people, thereby ensuring that our personnel are effective.”

However, he explains that mines have to employ more management personnel, such as mine captains and section managers, owing to regulatory requirements, and doing so makes the operating structure cumbersome. “For example, if you have to divide five pieces of equipment among three supervisors, the equipment starts to lose its effectiveness.”

PLANT CONSTRAINTS?
Joubert asserts that the most significant challenge at Two Rivers is the capacity constraints of the processing plant: “We are limited by the amount of tons it can treat, which is about 270 000 t/m. However, we have exceeded that by far and are doing very well with the optimisation processes at the plant.”

Uys says that, some months, the plant processes more than 300 000 t of ore while maintaining high levels of PGMs recovery. “In fact, it is targeting PGMs recoveries of 90%.”

He explains that mechanised mining often results in some dilution of the grade of the ore recovered, owing to the increased amount of unavoidable waste included.

“Yet, despite these challenges, the processing plant team can still achieve recoveries of 90% and are not resting on their laurels, as they are continuously looking at ways of treating greater volumes of ore and increasing PGMs recovery.”

Uys and Joubert highlight that feasibility studies are under way to assess the possibilities of expanding the capacity of the processing plant.

Joubert asserts that the studies “are looking promising”, as the plant could increase its capacity by 50 000 t/m, with little capital expense, by introducing a second secondary mill.

“We can easily cater for [increased plant capacity] by sinking shafts a bit faster and deploying an additional two fleets underground.”

Currently, shaft sinking at the mine takes place purely to maintain and not increase production, Joubert says. “We sink only half a level or a full level a year, within the boundaries of the capital allocation, because we are already exceeding the capacity of our processing plant. To do any more capital work will create a stockpile that cannot be treated.”

Uys points out that the project’s approval will depend on the price at which ARM can sell its PGMs.

“We have been considering increasing the capacity of the plant all along, but now there is a greater sense of urgency with the additional footprint available to us,” he told Mining Weekly, referring to ARM’s announcement at the end of last year that it would grow its stake in Two Rivers from 51% to 54%.

“We have come to an agreement with Implats and are finalising the Section 11 and Section 102 applications. Once these have been incorporated into the mining licence for Two Rivers, the footprint of the mine will be expanded to more than double its current size,” Uys concludes.

Pending approval of the Section 11 and Section 102 applications to incorporate the Tamboti block into the Two Rivers mining licence, the agreement with Implats will increase ARM’s stake to 54% and will more than double the footprint of the mine.